A Closer Look at Cloudflare’s Speed Test
With internet usage shifting from office districts to homes across the globe, understanding how your connection handles the new load is increasingly important. Cloudflare has made its speed test tool generally available at speed.cloudflare.com, aiming to offer more than a single score. The tool tries to explain what is measured and how the numbers are calculated, and it allows you to export raw data for your own analysis.
The test is built from three components — download, upload, and latency-related measures — each designed to reflect a distinct aspect of your connection quality.
Measuring Download Throughput
Download tests start with very small files, around 10KB, and scale up as the test progresses. Small file transfers are a realistic approximation of webpage loading, which typically involves many lightweight assets like images, stylesheets and JSON payloads. The tool displays the measured speeds for each file size so you can see how performance evolves as the file grows.
Moving to larger files reveals your actual bandwidth ceiling. The tool works up to the minimum file size needed to accurately measure full throughput, avoiding wasted data. This is necessary because TCP’s slow start mechanism caps throughput on small transfers; only larger transfers show the speed your provider quoted you when you signed up. Unsaturated big-file throughput is the number that matters for downloading an almost 100GB game or determining the maximum video resolution you can stream smoothly.
Upload Speed, Reported as p90
Upload speed is the reverse: data travels from your browser to the internet. This metric matters most on video calls, as both audio and video quality depend on how quickly your microphone and camera feeds get out to others. Similar to downloads, the test ramps upload sizes until it saturates your uplink.
Connection speeds are never fully stable. Latency and packet loss fluctuate throughout any session, so what you see at any single instant might not reflect your typical experience. For that reason, the tool reports the 90th percentile (p90) of measurements rather than the maximum. This discounts brief peaks and provides a more conservative, realistic estimate of sustained performance.
Latency and Jitter for Real-Time Media
Speed on its own does not paint a full quality picture, especially for videoconferencing. Latency is the time a packet takes to reach a remote service and come back. High latency delays your voice on a video call, but constantly changing latency creates a worse experience. Jitter, which measures variation between consecutive latency readings, captures that inconsistency. Low jitter keeps the delay steady, allowing media streams to remain intelligible throughout the conversation rather than falling in and out of sync.
Transparency, Private by Default
Cloudflare designed this tool so users can click into any measurement to see its average, median, minimum, maximum and related data points. There’s also an option to download the raw measurement file to inspect the underlying numbers.
The entire backend runs on Cloudflare Workers, moving all benchmarking logic to the edge and browser with no supporting servers. Cloudflare has also open-sourced the code in its worker-speedtest-template repository on GitHub. The company has stated that collected performance data is anonymized, is used to guide capacity decisions and peering choices, and is not sold to third parties. The tool’s treatment of network performance as layered data rather than a single ratio is its main advantage over existing test services.
